Golf ball

Abstract

A golf ball (1) comprises a core (3) and a cover (5). The core (3) has a six-layer structure having first to sixth layers (7) to (17). A value of (T1/T2) is greater than 2.10 and is equal to or smaller than 2.50, wherein time series data on force in a z direction which is applied to a load cell provided on a back face of a collision plate inclined by 22 degrees with respect to a horizontal direction when the golf ball (1) impacts the collision plate at a speed of 35 m/s in a vertically upward direction are represented by Fn(t), time series data on force in an x direction are represented by Ft(t), a time taken after a start of the impact before the Fn(t) is first changed from a positive number to zero is represented by T1 and a time taken after the start of the impact before the Ft(t) is first changed from a positive number to a negative number is represented by T2. The golf ball (1) has a higher back spin rate during hitting on the same conditions than that of a conventional golf ball.

What is claimed is:  
     
       1. A golf ball comprising: 
       a core, wherein said core is formed by crosslinking a rubber composition, wherein said rubber composition comprises a base rubber, a co-crosslinking agent, organic peroxide and a filler; and  
       a cover formed of a synthetic resin, wherein the modulus of elasticity of said cover is from 200 to 450 MPa;  
       wherein the amount of compressive deformation of the core is larger than 3.6 mm; and a value of (T 1 /T 2 ) is greater than 2.10 and is equal to or smaller than 2.50,  
       wherein a direction of a counterclockwise rotation by 22 degrees with respect to a vertically upward direction is set to be a z direction, a direction of a counterclockwise rotation by 22 degrees with respect to a horizontally rightward direction is set to be an x direction, time series data on forces in the z and x directions which are applied to a load cell provided on a back face of a collision plate having a surface extended in the x direction when the golf ball impacts the collision plate in the vertically upward direction at a speed of 35 m/s are represented by Fn(t) and Ft(t) respectively, a time taken after a start of the impact before the Fn(t) is first changed from a positive number to zero is represented by said T 1 , and a time taken after the start of the impact before the Ft(t) is first changed from a positive number to a negative number is represented by said T 2 .  
     
     
       2. The golf ball of  claim 1 , wherein said core comprises a first spherical layer and a second layer surrounding said first layer, 
       wherein the modulus of elasticity for said first layer is 20 to 60 MPa and the modulus of elasticity for said second layer is 25 to 70 MPa.  
     
     
       3. The golf ball of  claim 2 , wherein 
       wherein the thickness of said first layer is 5 mm to 10 mm, the thickness of said second layer is 1.0 mm to 3.0 mm, and the thickness of said cover is 1.5 mm to 3.0 mm.  
     
     
       4. The golf ball of  claim 2 , further comprising a third layer surrounding said second layer, 
       wherein the modulus of elasticity for said third layer is 35 to 100 MPa.  
     
     
       5. The golf ball of  claim 4 , wherein the thickness of said third layer is 1.0 mm to 3.0 mm. 
     
     
       6. The golf ball of  claim 4 , further comprising a fourth layer surrounding said third layer, 
       wherein the modulus of elasticity for said fourth layer is 40 to 140 MPa.  
     
     
       7. The golf ball of  claim 6 , wherein the thickness of said fourth layer is 1.0 mm to 3.0 mm. 
     
     
       8. The golf ball of  claim 6 , further comprising a fifth layer surrounding said fourth layer, 
       wherein the modulus of elasticity for said fifth layer is 80 to 200 MPa.  
     
     
       9. The golf ball of  claim 8 , wherein the thickness of said fifth layer is 1.0 mm to 3.0 mm. 
     
     
       10. The golf ball of  claim 8 , further comprising a sixth layer surrounding said fifth layer, 
       wherein the modulus of elasticity for said sixth layer is 120 to 300 MPa.  
     
     
       11. The golf ball of  claim 10 , wherein the thickness of said sixth layer is 1.0 mm to 3.0 mm. 
     
     
       12. The golf ball of  claim 1 , wherein said value of (T 1 /T 2 ) is from 2.20 to 2.50. 
     
     
       13. The golf ball of  claim 1 , wherein said value of (T 1 /T 2 ) is from 2.20 to 2.42. 
     
     
       14. The golf ball of  claim 2 , wherein the modulus of elasticity for said cover is 350 to 450 MPa. 
     
     
       15. The golf ball of  claim 2 , wherein each of said first and second layers comprises polybutadiene.